Family Reunification and German EU Blue Card

I have a German EU Blue Card and I would like to know if I can invite my long-term partner to accompany me in Germany. We have been together for 12 years and we are not married. On the international EU Blue Card website it says you can with proof of long-term relationship - (eu-bluecard.com/family-reunification/), however on the German Blue Card website there is no information about inviting an unmarried partner.